Hello and thank you for posting photos along with your question. Although the photos are helpful there is nothing that can take the place of an in person physical exam. That would be the only way to really be able to evaluate what is going on. If you noticed this 4-5 weeks out then there is a good chance it is a seroma especially if the lump is larger in nature. If you are feeling a small lump then this could be due to whats called "fat necrosis." All that means is some of the fat may have lost its blood supply and then it gets hard. A physical exam should be able to determine what the lump is due to and sometimes an ultrasound can be done to really be sure. If it is a seroma then it will need to be drained and this is usually easily done in the office. After draining it you will need to keep your activity at a minimum and keep that area nicely and tightly compressed for as long as you can without taking off the compression. The most important thing however, is to make an appointment with you plastic surgeon and let them evaluate you, diagnose you and recommend what the next step should be. I hope this helps!Ankur Mehta MD